August 31, 2012

Hurricane Isaac Reversed Flow Of The Mississippi River

Hurricane Isaac was able to make the Mississippi River run backwards for 24 hours after hitting the Gulf Coast this week.

The U.S. Geological Survey (USGS) instruments recorded the flow of the river, and found that it was running in reverse on Tuesday.

The flow reached nearly 182,000 cubic feet per second upriver, and gathered up a height of about 10 feet above average. The agency said that the average flow of the river is about 125,000 cubic feet per second towards the Gulf of Mexico.

"Although it doesn't happen often, hurricanes can cause coastal rivers to reverse flow," the USGS said in a statement. "Between the extremely strong winds and the massive waves of water pushed by those winds, rivers at regular or low flow are forced backwards until either the normal river-flow or the elevation of the land stop the inflow."

The agency said that as Hurricane Isaac pushes inland, it is causing storm surges in the Mississippi River as far north as Baton Rouge.

"This reversal of flow of the mighty Mississippi is but one measure of the extreme force of Isaac," USGS Director Marcia McNutt said in a statement. "While such events are ephemeral, they are yet another reminder of why we need to respect hurricane warnings."

This isn't the only time the Mississippi River has been turned upside down due to the force of a hurricane. In 2005, when Hurricane Katrina hit the coast, it also reversed the flow of the river, pushing waters 13 feet above its normal level that year.

The USGS also said that Hurricane Isaac is causing coastal rivers in Louisiana to lose height, only to gain it back again soon after. It said this rising and falling of the rivers is a common occurrence during hurricanes and is caused by the spiral nature of the storms.

"As the winds sweep to the southwest, they force water out of the rivers, lowering their height," The USGS said. "However, once the winds complete their turn to the southwest, they begin back to the northeast, allowing the storm surge to raise the river levels."

The USGS has an extensive network of "streamgages" that are located through Louisiana and the rest of the U.S. These instruments record data like streamflow, river height, and even water chemistry.

Some of the streamgages transmit their data in real-time to satellites, updating with new information every 15 minutes.

This data allows the USGS, emergency managers and responders to have accurate and up-to-date knowledge of what the rivers and streams are doing.

"In fact, anyone can sign up to receive notices from USGS streamgages when waters are rising in nearby rivers and streams through a program called WaterAlert," USGS said. "It is a free service that allows members of the public to receive notifications about water levels at any of over 7,000 USGS real-time streamgages around the country."